Let A be a finite set of positive integers, and N = |A| be the size of A.
We shall say that A is pleasant if for all x,y ∈ A
x / gcd(x,y) ≤ N
(The gcd(x,y) -- greatest common divisor -- is the largest positive integer that divides both x and y.)
For example, suppose A = {2, 3, 4, 5, 6}. N = 5...